Electrically driven portable surface treating machines such as a sander, polisher, buffer and the like have an oscillatable platen which creates dust during use which is normally allowed to enter the ambient air in a work area. There has been a long standing need for improving the constructional arrangement of such machines so as to provide for the collection of such dust. A number of dust bags have been proposed but the proper support for such dust bags did not meet the requirements for successful use and sale of the machine. What was found wanting in the prior art was a support which holds the bag so as to not interfere with the operation of the machine during use yet which is readily detachable and easily replaced and properly positioned on the machine. The support must also permit emptying of the dust bag without removal of the support and at this same time be inexpensive and simple in construction.